Being able to update subjective values based on new information in decision contexts with uncertainty is an important aspect of adaptive cognition. By combining the assessment of updating behavior during a gamble bidding task with measuring frontoparietal activity using functional near-infrared spectroscopy (fNIRS) in older adults (66 to 83 years), this study shows preservation but also impairments of updating behavior in old age. In line with previous results observed in younger adults, older adults update values when new information helps to reduce uncertainty; however, they also update values non-normatively in situations when this is not the case. Using a Bayesian model to fit the behavioral data and to conduct a model-based analysis of brain activity indicate that value updating in older adults is mainly driven by the process of expectation violation instead of belief updating. Older adults with greater expectation violation-related brain activity in the left dorsolateral prefrontal cortex (DLPFC) showed greater deviations from normative predictions in their updating behavior. Considering these results together with earlier findings in younger adults as well as results from secondary analyses directly comparing older with younger adults reveals reduced sensitivity to uncertainty reduction in older adults and age-related differences in subprocesses during valuation and their brain correlates.